Blower control



April 15, 1947. w. A. HAUGSTED 2,418,835

I I BLOWER CONTROL Filed Aug. 22, 1944 3 Sheets-Sheet l v PRESSURE I N VEN TOR:

William Haugsted ATTORN Y5 April 1947 v w. A. HAUG'STED 2,418,835

BLOWER CONTROL Filed Aug. 22, 1944 3 Sheets-Sheet 2 IN VEN TOR:

ATTD Eys W. A. HAUGSTED BLOWER CONTROL Filed Aug. 22, 1944 April 15, 1947.

3 Sheets-Sheet 3 INVENTOR:

W Lniam A H augs'ted.

mw. W

Patented Apr. 15, 194? UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 8 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to controls for centrifugal compressors or exhausters.

In the following specification reference will be made to the accompanying drawings in which:

Fig. l is a typical pressure-volume curve for a centrifugal compressor or exhauster having thereon isodynamic lines showing the power consumed by the machine.

Fig. 2 is a typical layout for a centrifugal compressor or exhauster system in connection with which the present invention is used.

Fig. 3a is an instrument and Wiring diagram of a portion of a centrifugal compressor or exhauster control embodying the present invention; and

Fig. 3b is a continuation of Fig. 3a showing the remainder of the instruments and wiring.

Reference will be made hereinafter to the term blower, and it will be understood that that term is generic and applies equally to a centrifugal compressor or to a centrifugal exhauster.

In regulating blowers, it is customary to provide a valve [5 to regulate the supply of air to the blower. If desired the valve [5 may be replaced with adjustable guide vanes which serve the same purpose.

For each position of the valve H5 or guide vanes, there is definite pressure-volume characteristic curve. Such a set of curves is shown in Fig. 1, in which the curves a, b, c, d and e represent successively greater openings of the valve 35 15, the curve e representing the fully open position of the inlet valve.

If at any time insufi'icient air is available to the blower for any given opening of the valve l5,

a serious vibration of the machine will occur. 40

Such a vibration due to lack of air passing through the machine is known throughout the industry as pumping. The points at which such pumping occurs for various openings'of the valve l5 define what is known as the natural pumping 45 curve, shown on Fig. 1 at 1.

Whenever the operation of the machine approaches the natural pumping curve I, it is necessary to permit additional air to pass through the blower. This air is usually supplied by a bleed valve leading into the pumping line. In the case of an exhauster, such a valve is located on the inlet side of the machine so as to let more air into the system which passes through 'ever, the inlet side of the machine is open to the atmosphere, in which case the bleed valve must be placed on the exhaust side of the machine so that a portion of the air pumped into the machine will bleed out through the bleed valve into the atmosphere thus permitting more air. to go into the machine and eliminating pumping.

One object of the present invention is to provide a centrifugal blower system which will operate constantly beyond the pumping curve.

Another object is to provide a blower system which will reduce fluctuations in the quantity of air delivered.

A further object of the invention is to provide a blower system which will operate constantly at near maximum efficiency.

A still further object of the invention is to provide a blower system in which the fluctuations of the bleed valve are reduced to a minimum;

A still further object is to provide a blower system in which the quantity of air bled into the blower will remain substantially constant through a limited range.

A still further object is to provide a blower system in which the bleed valve remains in fixed position over a predetermined range of pressure.

A still further object is to provide a blower system in which the bleed valve remains in a fixed position over a predetermined range of de- 0 livery volume.

A still further object is to provide a blower system in which the bleed valve remains in fixed position over a predetermined range of pressur and volume.

A still further object is to provide a blower system which will automatically start bleeding air as the conditions of the operation of the blower approach the natural pumping curve.

A still further object is to provide a blower system in which the bleed valve is automatically reset to a different fixed position when either limit of a predetermined range of "volume is reached.

A still further object is to provide a blower system in which the bleed valve is automatically reset to a different fixed position when either limit of a predetermined range of pressure is in connection with the accompanying drawingsillustrate one form of the invention.

In its broad aspect the invention comprises a bleed valve placed in the inlet of a centrifugal the blower. In the case of a compressor, how- 56 exhauster or in the outlet of a centrifugal com 3 pressor with means to open the bleed valve at a predetermined point on the pump characteristic curve to permit additional air to pass through the machine.

Referring to Fig. 2 there is shown a diagrammatic view of a blower assemblyincluding a portion of the controls. The blower ill, actuated by a constant speed motor ll, has an inlet pipe l2 and an exhaust pipe l3 which together form a conduit for the passage of air from a source through the blower. The inlet pipe l2 has a valve IE or adjustable guide vanes comparable to ,a valve located in the blower inlet to regulate the flow of air to the blower. The valve or guide vanes l5 may be adjusted through a pneumatic cylinder H which contains a piston (not shown) which operates a piston rod 18. The piston rod l8 moves upwardly to adjustthe position of the guide vanes or valve IS. The cylinder I? is maintained under air pressure through pipeline l9. The jposition of the piston in th cylinder is governed by air pressure on a diaphragm 2 which is supplied from a variable pressure source throilgh a transfer valve 22. Pressure in the transfer v lve 22 may be regulated by a handwheel' 23 and the pressure indicated on an indicater--24,

If desired a static pressure indicator (not shown) may be placed in the inlet pipe l2 (or the exhaust pipe l3 in the case of a compressor) and the pressure within the pipe l2 or l3 used with an actuator at valve 22 to automatically set the valve 15 t0 the desired position. Setting the valve l to any defin te position will cause the blower ID to operate on a characteristic curve such as shownat a, b, c, d, Fig. 1 each setting of the valvev ,5 giving a separate characteristic curve. thev volume, of air passing into the blower is decreased and the machine approaches the natural pumping curve 1, it is necessary to supply additional air to the blower in order to avoid pumping or vibration. In the case of the eX- hauster shown in Fig. 2, this i done by a bleed valve 3}) which leads into the inlet pipe of the biower; The setting of the valve 31), is governed byla pneumatic. cylinder 3i, which contains a piston (not shown) having a piston rod 32 the moveqieht of which actuates the valve. The control of the air to the diaphragm 34 is effected through a pipeline 36 and transfer valve 35 by means. of the apparatus shown in Figsl3u and 3b, to bode.- scri d below.

Referring again to Fig. 1, it will be, noted that the characteristic curves a to e, inclusive, as well as. the natural pumping curvel, are crossed by a plurality of curves ml to 21.3, inclusive. Each of the curves ml to m8 are isodynam ic lines .or lines of equal power for various operating condi of the machine, the curve ml representmg the smaller amount of power and increasing t'o'avalueof m8.

In order to reduce the fluctuations and increase thev general eificiency the system disclosed, the present invention contemplates gradually openregime 'bleed valve. when the volume being pumped diminishes to a point where the machine: is operating close to the natural pumping curve, and continuing to open the bleed valve until the machine is operating at a'point far enough away from the natural pumping curve a to preclude fluttering of t e valve between. open and shut p s tive At hi a n themed va veseas can v t mane t e e f e bleed a su siegr; can firs amo t f air ie e' he v i m- If the machine should continue after the bleed valve is locked to move away from the natural pumping curve a point may be selected at which the bleed valve begins to shut, such a point being designated the shut position of the valve. When the shut position of the bleed valve is reached, the bleed valve is gradually closed until the operation of the machine again passes the locked position at which point the bleed valve is again locked in fixed position and bleeds a substantially constant amount of air into the system until such time a the operation of the machine reaches the open position of the valve or the shut position.

By way of example, and to simplify an explanation of the apparatus shown in Figs. 3a and 31), points may be chosen on one or more curves of the diagram Fig. l in which the bleed valve will open, loci; and shut. On the curve a, for example, it might be desirable to open the bleed valve when the power consumed drops to the value ml, lock the bleed valve in fixed position when the value of power consumed reaches the value m2 and start shutting the bleed valve when the value ofpower increases to m3.

Referring to Figs. 3a and 3b, which show the apparatus used to regulate the bleed valve in the manner outlined above, it will be seen that the power for the system is supplied from two sources, the first is a three-phase power system used to operate the blower l9, having potential leads 4i and current lead 40 which are connected to a plurality of watt-meters Al to A4 in a manner such as to indicate the power consumed by the blower Hi. A second source of power is from a pair of power lines 58 controlled by a switch T, the power from lines 58 being used to actuate the various apparatus other than the blower l0 and watt meters Al to A4.

The watt meters Al to A4 each have a minimum and a maximum switch thereon, the minimum switches being labeled m l to 1224, which are adapted to open upon an increase in power above that for which the switch is set, the maximum switches being labeled m5 to m8, inclusive, and are adapted to close upon the increase in power above that for which they are set. The switches ml to m8 are set for powers corresponding to the isodynarnic lines ml to 7128 of Fig. 1. The switches ml to m8, inclusive, control the action of relays Bl to B3, respectively, the power for the relays bein obtained from the line 58. The relays Bl to. B8 each has. two contact switches, one of which opens upon energization of the relay and one of which closes upon energization of the relay.

The relays Bl to B8 have switches thereon numbered 42 to 49, inclusive, which control circuitsMll! to M and 59 to 51 which control circuits MLS to M88. T e circuits M10 to M89, are each closed when the switches ml to m8, respectively, arev actuated due to a decrease in power, while the circuits MIS to MBS are each closed,

when the switches ml to 121.8, respectively, are

actuated due to an increase in power. The cir-. cuits Mil) to M80 are connected to terminal board Tl while the circuits MlS to MBS are connected to both terminal; boards T-2 and T-3.

Three terminal boards Dl, D2 and D3. are 10-. cated adjacent the boards Tl, T2 and T3 to provide for three different operating conditions of the machine, with a gang switch C being used to seiectthe particular conditionunder which it is desired to havethe machine operate. In the example given above, (column 4, linesl4 to 24) It; it: is desired to open the bleedvalvefor a value of; power m1 on curve a, MN] on board Tl would be connected by an electrical jumper to the terminal aOl on board DI. Similarly, the terminal M2L on board T3 would be connected by jumper to the terminal aLl on board Dl and the terminal M3S on board T2 would be connected by jumper to aSl on Dl. Similar connections are made from the operating points selected on the other characteristic curbes b, c and d between the boards Tl T2 and T3 and the boardDl Lines leading from the terminal boards Dl, D2 and D3 lead to a gang switch C thence to a terminal board E. The gang switch C selects which board DI, D2 or D3 it is desired to use. From the terminal board E the connections run to a plurality of relays F8, F6, F4 and F2. The relay F8 is intended to control the three positions, namely, open, locked and shut in the range of the d curve and has thereon three switches 62, 63 and M to control respectively the open, locked and shut positions. The relay F5 controls the open, locked and shut positions for the range of the curve and for that purpose has switches 65, 66 and 61. The .relay F4 controls the open, locked and shut positions for the range of the curve I) and has for that purpose switches 68, 69, ill. The relay F2 controls open, lock and shut positions for the range of the curve a for which purpose it has switches l l, l2 and I3.

Relays F3, F6, F4 and F2 are controlled by pressure switches Gd, Gc, Gb and Ga, respectively, through relays Fl, F5, F3 and Fl. The switches Gd, Gc, Gb and Ga are arranged to close when pressures on the diaphragm 23 raise to or exceeds the pressure necessary to give the characteristic curves d, c, b and a, respectively. When the pressure on the diaphragm 20 raises to a point sufficient to give the characteristic curve a the pressure switch Ga energizes the relay Fl. Energization of the relay Fl completes the circuit through a switch 15 on the relay Fl, actuating the relay F2 and closing switches ll, 12 and 13. When the pressure on the diaphragm 20 raises to a pressure sufficient to give a, characterized curve I) the pressure switch Gb operates to energize the relay F3. Energization of the relay F3 opens the switch '16 and closes the switch 11. ()pening the switch l6 breaks the circuit to the relay Fl while closing the switch ll energizes the relay F4. De-energizing relay Fl opens the switch "l and de-energizes the relay F2 breaking the contacts between the lines a0, 0.1, as and the line 0, l and s. Energization of the relay F4 completes the circuit across the switches 68, 69, 19.

When the pressure on the diaphragm 29 reaches the value which gives characterized curve 0 the pressure switch Go is actuated to energize the relay F5 which simultaneously opens a switch 1-8 and closes a switch 19. Opening the switch 18 breaks the circuit through the relay F3 de-energizing relay F4 opening switches 68, 69 and 19 while closing the switch 19 energizes relay F6, closing the switches 65, 66, 51.

When the pressure on the diaphragm '20 reaches a point necessary to give the characterized curve (1 the switch Gd operates to complete the circuit through the relay F1 and simultaneously opens a switch 80 and closes a switch 9|. Opening the switch 80 breaks the circuit to relay F5 de-energizing relay F3 to open switches 65, B6, Bl, and closing the switch 8| completes the circuit through the relay F8 to close the switches 62,63 and 64.

The switches Ga, Gb, G0 and Gd are mercury snap switches and are set to close the circuits therethrough at the characteristic curves a, b, c and 12, respectively, on Fig. l and to hold' the circuit closed until the pressure has dropped to the Values a, b, c, and d respectively.

In the example chosen above, it was desired to open the bleed valve on the curve a when the value of power reached ml. The connection was therefore made on the board Tl between the terminal Ml 0 by jumper to col on board DI, and between MZL on board T3 and aLl on board Di and between M3S on T2 and aSl on board Dl. When the machine is started, and. until the power builds up to the value ml, the switch ml on the wattmeter Al is closed, maintaining the relay Bl energized and sending the current to the line Mlll on board TI and aOl on the board DI and to the terminal (10 on the terminal board E, and. to the terminal a0 on the relay F2.

As the machine is then operating on the curve a by reason of the setting of the valve l5, the current will be closed across the switch Ga, energizing a relay Fl, completing the current across the switch l5 and energizing the relay F2. Energization of the relay F2 completes the circuit between a0 and O, which energizes a main coil MC of a relay HH locking the relay in energized position. Energization of the relay HI-I breaks the circuit to a switch 35 to extinguish a pilot light PL and simultaneously makes the circuit through switch 85 to light pilot light PO and to open a pair of solenoid valves RI and R2. Opening the valves RI and R2 starts air flowing from a pressure pipe 81 through valves 88, 89 through.

a needle valve 99, into the supply pipe 36 and to the diaphragm 34, Fig. 2. As the pressure builds up on the diaphragm 34 through the continued opening of the valves 93 and 89, the bleed valve 39 continues to open, permitting more air to pass into the intake of the blower, which causes. the machine to operate further away from the natural pumping curve I.

When the pressure-volume relationship builds up to a point where the power consumed is equal to m2, the switch m2 opens, ole-energizing the relay B2 closing the circuit across the switch 52 and energizing the line MZL on the board T3, and aLl on DI, since the latter two are connected by jumper. Current passes from aLl on board Dl through the gang switch 0 to terminal aL on board E and terminal aL on relay F2. Since the machine is operating on the curve a, the relay F2 is energized and the current passes into line L which energizes the relay Q'l. Relay Q] has four switch contact members 9|, 92, 93 and 94, switches 92 and 94 closing upon energization, and switches 9i and 93 closing upon de-energization of relay Q'l. Upon energization of the relay Q1, current passes from the line 58 through the switch 92 through a switch 95 on a relay Q5 to energize a relay Q2. Energization of the relay Q2 closes the circuits through switches 96 and 91 on that relay. Closing the switch 91 sends current from the line 58 through the unlock coil UC'pf the relay HH and through the unlock" coil of relay I-I, de-energizing the relays H and HH and breaking the contact across the switches 86 and llll. Breaking the contact across the switch 86 closes the valves RI and R2, and extinguish'cs pilot light PO while breaking the current across switch lOl closes valves SI and S2 and extin guishes pilot light PS. The bleed valve 39 is thus locked in substantially fixed position in which a set amount of air passes therethrough.

Closing a switch 96, energizes the relay Q4, which closes a switch 99. Closing of the switch 98 completes the circuit through the main coil MCI-of relay Q6, locking fit in energized :position anctbre'aking the circuit' acrossswitch de-renergizing the'relays Q2, Q4 and Q3. 'Theirelay Q4 is necessary in the circuit to insure the operation of the unlock :coil UC of the :rlay lI-II-I before the current is broken across the switch 95.

Ifthemach'ine'continuesai terilockingthe'bleed valve 38 in mixed position to move away from the natural pumping curve "=1 du'e to external causes, :power will build up until its value :equals m3, at which point the switch m3-on the wattmeter A3 opens, dropping the relay B3 and closing -the switch 54, completing the circuit to the line MSS on the 'tern'iinal board T2, to the terminal aS'l on the terminal board 'D l, through the ang switch C to the terminal as on terminal board E and on relay F2. Since the machine is still operating on curve a, the relay F2 will be energized, closing the circuit' across switch 13, which energizes the main coil MC of relay H, locking that relay in energized position. Energizing the relay 'H simultaneously opens -a switch um, extinguishing the pilot light .PL if that light is lit and closing the switch l-l. Closing the switch Ill-l energizes a pair of-solenoid valves SI and 82, opening valves Hi2 and 4 03, permitting the air to bleed =-out -from the diaphragm 34 through the needle valve 90 past the valves M2 and N33 to the atmosphere, thus-causing the bleed valve 30 to shut I gradually. Simultaneously, closing the switch fli'l lights the pilot light PS indicating that the bleed valve is shutting.

When the value of the current again drops to a value of m2, the switch m2 will close, opening the switch '52 and cutting off the current to M2L on board T3,-which cuts off the 'current through contactaL on relay F2 and to the relay Q1, closing the switches 91 and 93 on the relay Q1. De-energization of the relay Q! sends the current from the line 58 through the switch -93 through a switch i E on-a relay Q5 and energizes a-re'layQ-Lclosing a pa'iroii switches IFS-and I01. Closing theswitch 411-! completes a-circuit through the unlock coil UC of both relays Hand l-IH unlocking those relays and die-energizing the solenoids RI, R2, SI and S2, and closing valves 88, 89, I02 and I03. Closing the valves -88 and 89 and'the valves T02 and 153, holds the -bleed valves 30' in 'fixed position and permits constant bleeding of air into the machine.

-Operation The points at which 'it is "desired to open, lock and shut the bleed valve are determined either from characteristic curves "such as are shown in Fig. 1,-or by experiment, andthe values of power at which each such change is to bemade is set-on the corresponding switches ml to m8. Electrical jumpers arethen connected between the terminal board '1! from the point at which it is desired to open the bleed valve on curve hand the terminal a'Ol on board DI and similarlyjbetween the points on the *board Tl at which it is desired toopen the valve 'onthe'curves b, c'and d and the corresponding terminals 501, 601 and 1101 on the board DI.

Electrical jumpers are also connected between the terminal points MIfS to 'MBS on-th'e board at which it isdesired to start shutting the valve 30 and corresponding points aSl, JJSI, 08! and as on the boa-rd DI.

Similarly, jumpers -'conn'ect -th'e points Mil. to MBL on the board T3 at which it is desired to effect locking of the ble'e'd valve in fixed "position 8 on each curve :to the corresponding points aL-l, bI l, 10111 and 1114 Ion the iterminalib card D l.

The blower .is started with the valve 'l5 shut position and the waive maintained shut till the blower :has attained substantially 'iull operating speed. After :the :blower has attained r1111 speed, the valve [5 is :set to "cause the blower to operate on any desired characteristic curve. dif :thgsetting of the bleed valve 15 is such as Ito scausethe machine to operate aabovethe characteristic curve a, the pressure from :the line 61 will actuate the pressure switch Ga, energizing the relay FI and closing the switch "[5, thus energizing the relay F2. Energization'of the relay F2 closes switches M, 12 and "13. Until the power being used by the blower exceedsth'at at which it is'desiredto open the bleed valve "38, the terminal (10 is connected to the power line 58 through the switch -42 and hence, when the :power falls 'below that point or, until it builds up to exceed it, with the blower operating between curves at and b, power will :be transmitted across the switch -11, :sending cur-- rent into the line 0 which energizes "the main coil MC of relay HH and locks it in energized position. Itwill be-noted that whereas'the switch Ga closes to complete the circuit across the switches H, 12 and 13 at apressure a (Fig. 1-), that it retains control until the operation of the machine decreases to a point Pat which it is operating oncurve a (Fig. 1).

Energizing the relay HH closes the switch 86 and energizes the solenoid valves RI and R2, causing the valves 88 and 89 to open and permit air from the pressure source 8"! :to fiow .past the needle valve 96 and gradually open the bleed valve 39.

When the current builds up :to the point where it "is :desired to lock the bleed valve, the line aL becomes energized, through sew-itch 5-2 sending current through the line .L to :energize ztherelay QT. Energization of the relay Q1 closes the switch 94, unlocking the relay Q5 and simultaneously closes the switch-92, sending current across the switch 95 of relay Q51, to energize the relay Q2.

Energization of relay Q2 'perm'its current to flow across the switch 91., which sends a current to :the unlock coilf-UC of theJelay-HH-and to the unlock :coil UC to "the "relay H. De+energization df the relay HH closes the valves 88 and 8 9, preventing further opening of the 'bleed valve while de-energization of the relay H closes the valves I'M-I03, preventing any closing of the bleed valve 33. 'The bleed valve is thus locked in fi ed position and bleeds a substantially .set amount of air into the machine, Energization or the relay 'QZ likewise closes ith'eswitch 96 which energizes the relay Qa, closing switch 98, energizing. the main coil MC, the relay Q5, llocking that relay in energized :pfositionland breaking the circuit to Q2.

De-energization of the relay "Q2 breaks the circuit across the switch 9 andcuts 01f currents to the coils ofrelays fl and shouldth'e power build up :due to changes in the operating conditions in the machine to the point at which it is desired to start shuttin the valve '15, the circuit 4S is energized, which transmits current across the switch -13, energizing the circuit S, which sends-current to the main coil MC of the relay H, energizing that relay and closing the switch liil. Closing the switch Hll energizes the solenoid valves SI "andSLopening the valves 'I stand ms, permitting-air to drain fromthe diaphragm 34 through the needle valve and es- As the bleed valve is gradually closed the power consumed decreases until it again passes the look point on the operation curve, at which point the line aL becomes tie-energized through opening switch 52, tie-energizing the relay Q! and completing the circuit across switches 9i and 93.

Completion of the circuit across the switch 9!- sends a current through the unlock coil UC of relay Q6, de-energizing the relay and completing a circuit across the switch 95. Completion of the circuit through the switch 93 sends a current through the switch H05, which is now closed and energizes the relay Q! Energization of the relay Ql completes the circuit through a switch ill! to unlock the coils UC of both relays HH and H, de-energizing those relays and closing the solenoid valves RI and R2 and SI and S2 to again lock the bleed valve in fixed position.

It will be noted that the bleed valve 39 is locked in fixed position when in the process of either opening or shutting, and the operation moves across the lock point.

Pilot lights PO, PL and PS are placed in the circuits between the relays H and HH and the valves RI, R2, and SI, S2 to indicate whether the bleed valve 30 is opening (PO) shutting (PS) or locked (PL).

If the valve 15 is moved to a position where the machine is operating on curve I), the pressure switch Gb then cuts in, breaking the circuit through the switch Hi to the relay F! When the circuit through the switch '35 is broken due to the closing of switch Gb when the pressure reaches or exceeds curve b, the relay Fl drops, opening the switch 15 and breakin the circuit to the relay F2, disconnecting switches I I, 12 and 13.

Energization of the relay F3 also closes switch 71, actuating the relay F4 to close switches 68, 59 and Ill. Since the switches H, 12 and 13 are cut out upon energization of the relay F3 and switches 68, B9 and iii are out in, second set of predetermined points at which it is desired to operate the valves R! R2, Si and S2 on the curve I) will assume control to energize or de-energize the lines 0, L or S. The circuits 0, L and S actuate the relays H and HH, controlling the valves RI, R2 and SI, S2, respectively, in the same manner as set forth for curve a.

When the power builds up sufiiciently to cause the machine to operate on or above the characteristic curve 0, the current is completed from the switch Go to the relay F5, breaking the circuit through the switch 18 to both the relays FI and F3 at the same time completing a circuit to the switch 79 to energize the relays F6, closing switches 65, 66 and $1. Breaking the circuit to the relay F3 opens the switch 71 and breaks the circuit to the relay F4, opening the switches 68, 39 and 10. When this condition exists, a, third set of predetermined points chosen to operate the open, shut and lock positions of the valve 31! on the curve control energization or de-enering the circuit to the relays F5, F3 and Fl, and

.10 making the circuit to the relay F8. Breaking the circuit to the relay F5 de-energizes the relay F8, opening the circuit switches 65, 66 and 61. Under these conditions, a fourth set of points chosen to operate the opening, locking and shutting of the valve 30 for the curve 11 actuate the relays HH and H across closed switches 62, 63 and 64 in the same manner as described for curve a, to control the valves Bi and R2 and SI and S2.

The pressure switches Ga, G1), G0 and Gd are designed to close at one pressure, and open at a lower pressure. Thus the switch Ga is adapted to control the operation of the machine between the curve a and b; the switch Gb is adapted to control the operation between the curve I) and c; the switch Go is adapted to control the operation of the machine between the curve a and d; and the switch Gd is adapted to control the operation from the curve 11' to the maximum curve e. Thus when the bleed valve is locked, it remains in fixed position over a given range of pressures and over a given range of volume andmay be said to remain constant over a given area on the pressure-volume curve, such typical areas being shown shaded in Fig. 1.

It is obvious that the blower herein can be made to operate on any intermediate curve between curve a and the curve c, (Fig. 1), as well as exactly on the curves a, b, c and d. For increasing pressures, the pressure switch Ga assumes control of the operation as the pressure reaches curve a and retains control until the pressure either increases to curve I) or decreases to curve a. Pressure switch Gb assumes control at curve I) and retains the control until the pressure either increases to characteristic curve 0 or decreases to curve b. The pressure switch Gc assumes control at c and retains control until the pressure either increases to curve 0. or decreases to the curve 0, and the pressure switch Gd assumes the control of the machine at the curve d and retains it for all greater pressures or until the pressure decreases to curve 01'. In reducing the pressures, the pressure switch d will retain control until the pressure decreases to the characteristic curve 01 at which point control is transferred to Go. The pressure switch Gc retains control until the pressure decreases to the curve 0 at which point control is transferred to Gb. The pressure switch Gb retains control until the pressure decreases to curve b at which point control is transferred to Ga and the pressure switch Ga retains control between the curves b and a. The machine is not operated below curve a.

The shaded areas of Fig. 1 show a complete typical layout at which it may be desired to efiect changes in bleed valve position. Until the power consumed by the machine reaches the valve of mi, Fig. 1, and with the valve I5 opened,,so that the machine is operating between the curves a and b, the bleed valve will be open and will start shutting when the power reaches the value of 1123.

As the valve I5 is opened, the point ml continues to retain control of the opening of the bleed valve 30 until the characteristic curve 11 is reached. At this point, pressure switch Gb cuts in and the control of the bleed valve is switched from power value ml to power value 1123. Since the switch Gb cuts in onthe curve Z) and cuts out on the curve b, raising the pressure or lowering it on either side of the line b, fails to throw control back to the switch Ga until pressure b is reached, thus preventing fluttering of the bleed valve.

Having thus described the invention, it will'be 1-ealizedthat it is susceptible to various changes b Letters Patent is:

1. A. blower having an inlet pipe anexhaust pip said-pipe forming aiconduit, an. inlet valve in. said conduiavariation of said inletvalve being adapted to varythe pressure-volume characteristic curve. of said blower, said blower having; a point on each characteristic curve. at which pumping occurs,v and a. bleedvalve in said conduit adapted,- upon opening, to cause. additional air to pass through said. blower, in. combination. with. a regulator for. said'blowensaid. regulator. comprisins. meansto gradually opensaid bleed. valve as the operationof the. blower approaches the naturalpumping curve,-.means to gradually shut the bleed. valve whenv the. operation. of the. blower has moved away from the. pumping curve to a definite amount,.means to look. the bleed. valve ini fixed. position as. the operation: of-v the blower passes. a point intermediate? that at which the bleed valve starts to open. and that atwhich it starts to shut, and means. to vary the points at bleed valve. openingv into said conduit. and adapted. upon opening, to. cause more air topass through. said blower, means. actuatedzby adrop in power being consumedby the. motor below a predetermined minimum tostart opening. saidbleed valve at a predetermined. control: valve. setting, means actuated by an increase of power above a predetermined. maximum: to. start Shutting; said bleedvalve, and meansactuat'ed. by. either a drop inpower or anincreaseinpower to lock saidbleed valve. in fixed position. at apredetermined point between theiopeni'ng and shutting, positions.

3..In a. stable operating pumping system. a blower,. power. means for driving. the blower, means for, varying the. inlet. flow to. the. blower to vary the pressure-volume operating character.- i'stice curve thereof, the blower having. a. point on. each. characteristic. curve. at which pumping occurs, abled'val've for admitting. ad'ditibnaLair to theblower, servo mechanism adaptedlwhen en.- ergized to move, the bl'eed'val've. the opening and closing. directions respectively and when deenergized' to leave the bleed: valve locked in ad justed'position, control'meansfor. the servo mechanismv including. means operative. upon the operating. characteristic of the. blower approaching the pumping curve to energize. the servomechanism to causeLopening of the bleed valve,. means operative upon the blower operating, characteristics movingaway a predetermined. amount from the pumping curve. to. energize the. servomechani'sm to cause closing of. the bleed valve, the operating p'oints ofsaid' control means being. spaced apart such that, the zone. between the operating points on the pressure-volume curves is. an appreciable portion of. the operating range of. the blower and means. operable upon the operating characteristics ofthe blower. reaching a median point between the. limits. of; said. zone. to deenergize the servo mechanismto. lock; the bleed .valve in adjusted position. until, either of; the operat- .ing, points for the: servo mechanism. is; again reached. due to. variation in. blower load. and means. responsive: to predetermined changes in the blower loadasthe inlet now is varied-to vary the operating points at which the bleed valve. is actuated 4..An automatic step bleed control for a. centrifugal blower toensure stable operation thereof,, comprising. in. combination with the. blower and power driving means therefor, at bleed: valve for. admitting additional air tothe. blower, servo mechanism for actuating saidbleed-valveinthe opening and closing direction, selective control means. for said servo mechanism adapted; when energized; to cause actuation: ofsaid servo mechanism and. when deen'ergized to: lock saidservo mechanism inadjusted position, and. means responsive tovariation in; input-power betweenpredetermined limitsz-operatively cemented: to; said control meansf'or energizing the: same, said: last named. means including means. operative upon diminution or. increaserof inputpower "beyond: said predetermined limits toenergize said: control means to cause the servo mechanism to adjust the bleed valve respectively inthe opening; and closing. direction to vary the blower load such that the input power approaches a median value between said predetermined power. limits, and means operable in response to the input: power attaining: said median value to deenergize said servo mechanismcontrolmeans to thereby leave saidbleed valve lockediin a fixed= adjusted position.

5.. An automatic blower control system: comprising. in: combination with thBfbIOWeI-Q a driving motor. for theblower, means for varying the-inlet flowof the-blower to vary the operatingpressurevolume characteristic curve; said blower having a point on each characteristic curve at which unstableoperation or pumping occurs, a servomotor actuatedbleedvalve for admitting additional air tothe blower to prevent pumping, said servosbeing of a type. when selectively energized will; move said. bleed. valvezin the opening and-closingdirect'ions respectively andwhen.deenergized-willleave the bleed valve locked in adjusted position, and control means for saidservomotor including a control element.mo.vable in HBCOIdBJHCGWithiVQIL ation inoutput power ofthe blower driving motor, a plurality of control devices: operatively" cone nected to said servomotor and engaged seriatim by said. control. element upon predetermined incrementsof changeinoutput power of saidblower drivingmotorrsaid control devices bein perative imgroupsofi three: to control. said servomotor a first. of. the. devices in. each said groupbeing operatiive upon. a predetermined. value: or. power to energize said. servomotor to. move: thebleed valve in the opening. direction, azsecond of; the-devices in eaoligroup being; operative at-apredetermined increment oi'ipower to energize the. servomotor. to move the bleedl'valvein the closin direction and the third device of. each-group being. operative upon the said. motor. output. power attaininga value intermediate the operative power value of the first and second devices to. deenergize the servomotor toitherebyleavethebleed valve locked in adjilstedlpositi'om.

GI The structure as claimed in. claim 5, including selector-means responsive to output.- pressure of the. blower for renderingsaid control devices roups sequentially. operative tocontrol'the servo.- motor as the blower load. is varied: by predeter+ mined increments.

'7. Thestructure; as claimedin claim:5-.in.which control device groups and said control device groups being '50 arranged that their respective points of operation occur in overlapping zones in the pressure-volume operating range of the blower as determined by the setting of the means for varying the inlet flow to the blower.

8. In a Stable operating pumping system, a blower, power means for driving the blower, means for varying the inlet flow to the blower to vary the blower load, a bleed valve for admitting additional air to the blower to eliminate unstable operation thereof, servomechanism f0! actuating said bleed valve in the opening and closing operation, 'said servomechanism including means responsive to a decrease in blower load below a predetermined minimum for causing a continuous opening of said bleed valve, means responsive to an increase of blower load beyond a predetermined maximum for causing a continuous c10 ing of said bleed valve, and means responsive to blower load attaining a predetermined value intermediate said predetermined limiting values for deenergizing said servomechanism and locking said bleed valve in an adjusted position irrespective of the direction of actuation of said bleed valve.

WILLIAM A. HAUGSTED.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,241,372 Guyer Sept. 25, 1917 1,097,298 Callan May 19, 1914 1,280,811 Moss Oct. 8, 1918 1,281,216 Schellens Oct. 8, 1918 1,325,255 Loewenstein Dec. 16, 1919 1,783,036 Crawford Nov. 25, 1930 2,000,721 Standerwick May 7, 1935 

